The present invention relates generally to inline power, and more particularly to a method and system for inline power allocation in applications such as Power over Ethernet (PoE).
Inline power (also known as power over Ethernet) is a technology for providing electrical power over a wired telecommunications network from power sourcing equipment (PSE) to a powered device (PD) over a link section. The power may be injected by an endpoint PSE at one end of the link section or by a midspan PSE along a midspan of a link section that is distinctly separate from and between the media dependent interfaces (MDI) to which the ends of the link section are electrically and physically coupled.
PoE is defined in the IEEE (Institute of Electrical and Electronics Engineers, Inc.) Standard 802.3af—2003, published Jun. 18, 2003 and entitled “IEEE Standard for Information technology—Telecommunications and information exchange between systems—Local and metropolitan area networks—Specific requirements, Part 3: Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications, Amendment: Data Terminal Equipment (DTE) Power via Media Dependent Interface (MDI)”, which is incorporated herein by reference. The IEEE 802.3af standard combines the transmission and reception of Ethernet packets with the transmission and reception of DC-based power over the same set of wires in a single Ethernet cable.
In accordance with the 802.3af standard, a PSE carries out an inline power detection process, and if successful, an inline power classification process. The detection process is performed to detect the presence of a PD at a network port prior to sending power to it and to prevent sending power and causing damage to devices that are non-compliant with the PoE standard. The classification process set forth in 802.3af, involves applying a voltage in a classification range to the PD. The PD may use a current source to send a predetermined classification current signal back to the PSE. This classification current signal corresponds to the class of the PD. Under the current 802.3af standard, the PD is classified as a member of one of a set of five classes shown below in Table I. While the 802.3af standard delivers different wattages, powered devices are often allocated more power than they need.
TABLE IPSE ClassificationCorrespondingClassCurrent Range (mA)Inline Power Level (W)Usage00-515.4default1 8-134.0optional216-217.0optional325-3115.4optional435-4515.4reserved forfuture use
In accordance with the 802.3af standard, power is provided up to about 15.4 watts. This may be enough power for a wide array of small devices, however, most laptops, personal computers, and other commonly networked devices require more power. The IEEE is therefore currently working to enhance the 802.3af standard to give networked devices more power. The new standard, IEEE 802.3 at (PoE Plus), is expected to extend the 802.3af standard power delivery capability to provide increased power to PDs (e.g., 30 or more watts).
It is therefore desirable to provide additional capability to allocate power to PDs and provide more power than is currently contemplated under the IEEE 802.3af standard, as well as additional and more precise power gradations.